Well Tracy did say it is normal for LOs to wake in the night and stay awake for long periods, so long as she's not crying just leave her to it. I know it doesn't feel nice to know she's awake all that time, missing out on her sleep, prob keeping you awake too, but apparently it's normal. When mine was doing it I felt really reassured reading that in the BW book. Mine was noisy though, chatting and singing etc, he would wake me with it so I would use a key phrase to tell him to go back to sleep.
Do you think there's a chance she is cold when you put her back to bed after her night feed? What about a hot water bottle or one of those microwave bag things to pop in her bed whilst she is out of it to keep it warm then remove it when you put her back in? It might be a bit more snuggly for her her and help her nod off? I did this every night feed when DS was tiny or he'd cry getting back into a cold bed and just not settle.